1. Field of the Invention
This invention relates to evaporators, and more particularly, to an evaporator for the treatment of contaminated wastewater.
2. Background Art
The disposal of contaminated wastewaters is of increasing concern due to ever tighter environmental regulations. Sources of such wastewaters are municipal landfills, petrochemical industries, paper industries, food industries, agricultural operations, remedial clean-up activities, and general industrial sources.
In particular, various kinds of wastes are buried in landfills that are known to produce noxious gases and condensates as the wastes decompose. In addition, water from rain and other sources percolates through the buried wastes, creating noxious leachates. These leachates are composed of a variety of chemicals, many of which are hazardous Escaping gases and liquids from such landfills are recognized as sources of pollutants that present health and environmental hazards and must be collected and treated.
It is common to dispose of the noxious gases produced by a landfill by withdrawing these largely methane gases and burning them in flares or other types of gas combustion devices. In most cases removal of the noxious gases from the landfill results in the production of liquid condensates. These condensate liquids together with the leachate liquids have traditionally been collected and hauled from the landfill site for disposal. This process of disposal is itself regulated and expensive as evidenced by the large amount of attention that has been given to the transportation and safe disposal of industrial waste liquids.
Prior art technology has been developed to deal with leachate and condensate disposal and includes the evaporation of the liquid leachate/condensate in a gasdirect contact evaporator, such as that taught in the patent to Young et al., U.S. Pat. No. 4,838,184. The Young patent teaches an apparatus and method for combusting a portion of the landfill gases and contacting a stream of the hot combustion products with the leachate liquids from the landfill to vaporize a portion of the leachate liquids. A drawback of the Young apparatus is its complexity and inefficiency, and the apparatus does not produce the desirable end result pollutant-free water vapor and an easily disposed of concentrated solids sludge.
Similarly, the patent to Duesel, U.S. Pat. No. 5,342,482 discloses an evaporation device for landfill leachate that has two zones, an evaporation zone in the upper section of the apparatus and a quiescent solids-settling zone in the lower section of the apparatus. This enables the simultaneous carrying out of evaporation and solids settling. It has been found, however, that the percentage of solids in typical wastewater streams is actually quite low, such that only after long periods of evaporation is it necessary to remove solids. In this situation it is preferable to merely pause the evaporation process for an appreciable period of time to permit solids to settle and then be removed. This non-simultaneous batch approach to evaporation and solids settling avoids the overly complex dual-zone apparatus of the Duesel patent.
Thermal efficiency has been found to be a key factor in the design of successful evaporator systems. Where landfill gas is the fuel, the fuel is essentially of no cost. The low-BTU nature of the gas, however, requires that as much as possible of what little energy is available be utilized for evaporation. Where purchased natural gas or propane gas is used as the fuel, expense becomes of primary concern and thermal efficiency is again a key factor. It would be therefore be desirable to have a disposal system that would overcome these and other limitations of the prior art systems. That is, it is desirable to have a disposal system which can efficiently and lawfully dispose of all leachate and gas condensates produced from any landfill in an apparatus, and which produces an easily disposed of solids sludge, while releasing only substantially pollutant-free water vapor which can be readily discharged in compliance with air quality standards and regulatory permits governing landfills.